NOTE: This article contains information about removing virtual machines in bulk directly
from PowerShell

Removing multiple virtual machines at a time can be done using Remove-ProvVM but if not done
with the correct syntax, it will generate errors indicating that the provisioning scheme already has
another task running.

 

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The proper way to call Remove-ProvVM using the results of Get-ProvVM is to use the comma
operator to force the result of Get-ProvVM to be an array.  The commands for this will use the ,()
syntax. time, and the entire list of VMs returned from the Get-ProvVM call will be passed as a parameter to
that one call.  Remove-ProvVM will then iterate through the list to remove each virtual machine as
expected.

The same cmdlets called without the ,() syntax will result in a separate Remove-ProvVM call for
each virtual machine in the provisioning scheme which will lead to the error that the provisioning
scheme already has another task running.

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Problem Cause

This is a symptom of how PowerShell works.  With incorrect syntax, calling Get-ProvVM and piping
the results to Remove-ProvVM will result in one separate Remove-ProvVM call for each VM returned
by Get-ProvVM, and may result in the error that the provisioning scheme has another task running.

This PowerShell help page describes the comma operator.
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_operators?view=powershell-7.4#comma-operator-